The best clues in identifying various internal structural abnormalities are usually provided by X-ray examination. Accurate radiographic imaging is a crucial tool in detecting the often minute anomalies that can signify the early stage of a disease or weakness. Early diagnosis of a problematic condition is frequently the most powerful weapon against that condition.
Breast cancer is an example of a disease that is diagnosed relatively easily through X-ray mammography. Radiological mammograms can show minute accumulations of calcium years before such abnormalities are detectable by other noninvasive means. The mammograms themselves, however, are simply descriptive instruments, and their usefulness is limited by their precision and accuracy and by their subsequent interpretation by trained medical lpersonnel.
Because each radiographic image is a product of the conditions present at the time the image was made, variations in successive images of a single target of examination are commonplace. The intensity of the incident beam, positioning of the beam and the target, nature of the target, and the time of exposure contribute to such variations. The detailed parameters of processing the resulting film to produce a visible image add a further source of variation. Standard procedure in radiographic imaging for medical and other purposes often requires interpretation of the image, subsequent in time, by a person remote in location from the technician who has produced the radiographic image of the examination target. Therefore, the interpreter is initially required to judge the accuracy of the radiograph and then to analyze the structures presented therein. The time, expense, and possibility of error involved in this practice highlight the need for a new method wherein radiographic images can be quickly and definitively assessed for image quality and clearly marked as meeting a given quality standard.
The current state of the art includes a Quality Test Standard for X-Ray Mammograms, U.S. Pat. No. 4,759,045. This patent teaches a test tab carrying particulate material to simulate the calcium deposits present in abnormal breast tissue. The tab is affixed to the breast prior to a mammogram and an X-ray beam is simultaneously directed through both the breast tissue and the tab. Small particles are included in the tab primarily to indicate the degree of resolution of the resulting image and larger particles are included primarily to indicate its degree of contrast.
U.S. Pat. No. 5,095,499 discloses an Oriented Mammography Phantom that includes test objects, such as fibers and particles, that function as a resolution capability test, an orienting feature for placement of the phantom in the X-ray beam's imaging plane and a series of holes defining a step wedge, for use as an X-ray quality test. The step wedge portion of the phantom is further defined as a linear array of holes of differing depths and differing radiolucency. The more radiolucent the region defined by the step, the darker the image on the exposed film. The use of progressively darker filters to form a step wedge is well known in the photographic art as a means of fine-tuning image contrasts. The phantom of the '499 patent is made of a radiolucent material of appropriate thickness to simulate the attenuation of X-ray beams that characterize the tissue being tested. Extra plates of similar radiolucent material are needed for use with the phantom if more attenuation, e.g., with a larger-sized examination target, is desired. A test film that utilizes the mammography phantom is compared, by the radiologist, to a reference film to determine the quality of the X-ray beam. Irregular image contrasts usually signal some type of equipment problems.
A test tool for X-ray system quality assurance and the manner of using the test tool are the subjects of U.S. Pat. No. 4,550,422. The test tool is a single device that contains a filter for altering an X-ray beam to produce an exposure at a certain density range, a step tablet for one step-at-a-time optical density comparisons, and written instructions on possible corrective action to be taken. The housing of the test tool contains two crossing channels, one for insertion of the test film and the other for the sliding step tablet. Matching is done by lining up the two so that their optical densities are visually similar.
In U.S. Pat. Nos. 5,063,583 and 5,276,726 to Galkin, the inventions relate to testing and standardization of film processors and correction of images for the effects of film processors. A body part is imaged and a test pattern is separately impressed on a single film. After development of the film, a visual comparison of the test pattern to a separate control pattern is needed to measure film processor performance. The image can be converted to an electrical signal and corrected for variations due to the film processor. The inventions are especially useful for accreditation of remote mammography facilities by a central governing board.
With all of the above patented devices and methods, the radiologist or other interpreter of the image is required to visually gauge the correctness of the exposure and processing steps that produced the radiograph, and to mentally adjust his analysis of the target image accordingly. Although the devices of the prior art have been found to be useful, there is a need for a more reliable alternative.
Therefore, it is an object of the present invention to provide a system and method that assesses radiographic image quality without the need for visual comparison of image patterns.
It is another object of the present invention to provide an easy to use, automated system that quickly assesses radiographic image quality.
It is yet another object to provide a permanent record, on a radiograph, indicating whether the film has undergone an assessment of image quality and whether the image quality was of a sufficiently high standard.